Radio-frequency electrical heating equipment



I5 Sheets-Sheet 1 Edmund C, an/

E. C. STANLEY July 4, 1950 l RADIO-FREQUENCY ELECTRICAL HEATING EQUIPMENT Filed Dec. l, 1947 E. C. STANLEY 2,514,101

RADIO-FREQUENCY ELECTRICAL HEATING EQUIPMENT July 4, 1950 3 Sheets-Sheet 2 Filed Dec. 1, 192,17

lwenlor Edmund C. San/ey A Hor/ley July 4, 1950 v E. c. STANLEY 2,514,101

RADIO-FREQUENCY ELECTRICAL HEATING EQUIPMENT Filed Dec. l. 1947 3 Sheets-Sheet 3 F/GS IIIHHIHIIHIUW umullmmmunu| nlmllllllmnl l 37. '-336 .55

Patented July 4, 1950 RADIO-FREQUENCY ELEoTnIcaL HEATING EQUIPMENT Edmund C. Stanley, Wokingham, England, as-

signor to Radio Heaters Limited, Wokingham, England, a British company Application December 1, 1947, Serial No. 789,062 In Great Britain January 6, 1947 (Cl. 21S-47) 6 Claims.

This invention relates 'to high frequency electrical heating equipment of the dielectric heater type in which the articles to be heated are placed in a heating chamber between the two heating electrodes.

In such apparatus, it is the usual practice to hinge the lid about an axis towards the back of the oven casing so that the lid is opened by being swung upwards. The upper electrode is generally arranged to be lifted with the lid to allow the charge to be removed from the heating chamber with the vminimum diiculty and obstruction.

It is usual to work with an air gap between the upper electrode and the charge to be heated so as to avoid contact beween that electrode and the charge. A parallelogram linkage is generally provided to raise and lower the upper electrode while maintaining the face of the latter parallel with the face of the lower electrode while the lid is closed and the air gap is adjustably by means of a screw brought out through the lid of the oven. This mechanism is easily arranged so long as the upper electrode is connected to earth and the lower electrode is operated as the live electrode. However, it is sometimes convenient to have the upper electrode live with the lower electrode earthed or with some oscillator circuits, to have both electrodes live. Hitherto, in such cases, a flexible conductor has been provided to convey the radio-frequency current to the -upper live electrode and the heating chamber has been of considerably increased height ref sulting from the fact that a parallelogram linkage is employed and the live electrode is carried on insulators .projecting down from the forward end of :the yparallelogram-i linkage.

The object vof the `present invention is to avoid the necessity of employing a flexible conductor which is a .source of trouble and to allow the heightbetween the lower surface of the movable upper electrode and the parallelogram linkage to be considerably reduced.

According to the invention, a parallelogram linkage is employed .and is .arranged so that the lower .longer member kserves as the connection bringing inthe radio frequency current from the high frequency generator .to the kupper .electrode while the upper longer member of the parallelogram is maintained `at ea-rth potential. The short vertical lin-k .at kthe front end connecting the upperand lower .members consists of an insulator. By keeping the lupper parallelogram member at ear-th potential, the mechanismfor adjusting the air VYgap .below the lire upper electrode is greatly simplied and may consist of a screwed rod operated by a knob on the top of the lid so that adjustment can be effected without opening the lid.

In order that the invention may be clearly understood and readily carried into effect, some forms of the novel arrangement will now be described, by way of example, with reference to the accompanying drawings in which:

Figure l is a central vertical section of one form of heating apparatus taken at right angles to the axis of the hinge of the cover;

Figure 2 is a vertical section at right angles to Figure 1 on the line IIe-.H in Figure 1; while Figure 3 is a circuit ydiagram showing a suitable lsimple generator circuit;

Figure 4 is a central vertical section of a modied and simple form of apparatus; and

Figure 5 is a sectional plan of the apparatus shown in Figure 4 taken on the line V--V in that ligure.

Referring to Figures 1 and 2, the hinged cover I is pivoted to the iixed casing 2 about a spindle 3. This spindle at each end is supported in two strips 4, 5 riveted to the inside o f the side wall 6 of the casing 2 at the points 1. It is prevented from axial movement by washers 8 and pins 9 passing through the spindle 3. The strip 5 is turned over at the top at IU and is braced to the strip 4 by a bolt I I and nut I2. The spindle 3 at each end also passes through an inclined strip I3 riveted at the points I4 to the inside of the side walls of the cover .or lid I so that the lid I can be turned upwardly about the spindle 3. When closed down, the lid I is retained by a catch Ia slidable on two guide rods A2o in the casing 2. The material to be heated is placed on the lower stationary electrode L5 and the upper movable electrode is shown at I6. The lower member of the parallelogram consists of a pair of parallel arms Il pivoted at .the back about a pin I8, whose axis is at a lower level than that of the hinge spindle 3. The upper parallelogram member consists of a single plate i9 of a downwardlyturned channel section and pivoted at its rear end to the framework ofthe lid I about a pin 20 lwhich is supported at a level above that of the hinge 3 in the side members of a bracket 2l secured to a plate 22 iixed in the upper part of the lid I so that the pivot pin 20 is `swung backwards when the lid I is raised. The upper movable electrode I6 is fixed to .the bottom of an insulator 25 which forms the :front linl of the parallelogram since the lower arms Il are pivoted at their front ends at the points 2.6 to brackets 2I carried by the electrode I6, while the upper parallelogram member I9 is pivoted at its front end on a pin 28 mounted in a bracket 29 Iixed at the top of the insulator 25.

The lower arms I1 at their rear ends have the pivot formed bya heavy transverse pin I8 fixed by screws 30 to a horizontal plate SI fixed to the outlet terminal 32 which extends through the top of an insulator 33 iixed at the back of the oven to the base plate 34. The live high frequency current connection to the upper electrode I6 passes in through the pillar 35 to the terminal 32 and through the arms I1 and brackets 21 to the electrode I6. The live electrode system is earthed when the lid I is opened by means of a strip 23 bearing at its upper end at 23a against the plate 22 fixed to the lid. When the lid I is raised, the strip 23 is swung out by the action of a coiled loading spring 23h surrounding the pivot pin 23o;V consequently the strip 23 `comes into contact with the pivot pin I8 which is thereby earthed. When the lid I is closed down, the plate 22 exerts a thrust on the top of the strip 23 at 23a, so that the strip is swung away from the pivot pin I8 linto the, position shown in Figure 1.

The gap between the electrodes I5, I6 is arranged to be adjusted when vthe lid l is closed down by rotating a knob, 36 pinned to a screwed rod 31 having a bearing in the top of the lid I so that the rod 31 is prevented from moving axially. The rod 31 is threaded into a nut 38 which can turn on the endsV of screws 39 secured in L shaped brackets 49 fixed to a channel-section arm 4I on whichtheupper parallelogram member I9 rests and which is pivoted about the same axis 29 as `the member I9. This arrangement enables the adjustment to remain set and undisturbed when the lid I and upper electrode IG are swung upwards. When this happens, the pivot pin 2l) as already mentioned is swung backwards, the insulator 25 tilted and the upper electrode raised so as to expose its under surface for cleaning. If a layer of material to be heated which is too thick is placed `on the lower electrode I5, the upper electrode I6 and the upperr parallelogram member I9 which is connected to it by the insulator 25 are free to ride up slightly while the lid I is closed downwithout straining any of the joints. y .K

In Figure '3 is shown a simple form of conven-j tional radio-frequency generator circuit, the electrode I9 and arms I1 being shown diagrammatically. The oscillator tube 42 is 'a triode with grid coils 43, 44 in series respectively with a resistor 45'and condenser 46. rThetank coil 41 and` condenser 48 are connected between the anode 49 of the tube 42 'and the filament cathode 59 which is earthedy 'at 5I while the high tension supply is connected to the anode 49 through the anode choke coil 52. The output coil 53 is coupled to thetank coil 41 and is connected to, the upper Velectrode I6 through the lower parallelogrammemblers I1.

In the m'o'died form vshown in Figures 4 and 5, the lower earthed electrode I is again supported on the oven base plate 34 and the upper live electrode VIcarries a stirrup-shaped bracket 54. on thetop of which is mounted the insulator 25. The electrode I6 is suspended on two fiat stripsA I1, I9 forming the lower and upper longer. members of the parallelogram linkage and pivoted'respectively at 26 and 28 to the electrode vIIS and thetop of the insulator 25. The lower strip I1 conducts the current to the live that of the hinge pin 20.

For raising and lowering the upper electrode I5, a mechanism is provided comprising a knob 35 fixed to a threaded spindle 31 engaging within a tapped boss 58 xed to the end of a transverse bar 59 which passes through the side plates of the bracket 55 and engages below the bar 59.

The spindle 31 is journalled and guided in a bush 69 in the top wall of the oven so as to be prevented from axial movement as in Figures 1 and 2 and when rotated, raises or lowers the bar 59 sol as to raise or lowervthe upper electrode I6. As before, the electrode is free to rise or float since the strip I9 is restingon the bar 59. A knurled nut 5I is provided to lock the spindle 31 in any desired position.

I claim:

l. In a high frequency dielectric heater, a stationary electrode, a parallelogram linkage having its members located in a plane at a right angle to the surface of said electrode and consisting of two longer members pivotally mounted on fixed pivots and an insulating link connecting the movable ends of said longer members, an adjustable electrode rigidly connected to said insulat-V ing link and mounted with its face parallel to the face of said stationary electrode and electrically connected to the movable end of said longer parallelogram member which is nearer to said stationary electrode and a ground connection for the 'other of said longer parallelogram members.

2. In a high frequency dielectric heater, a metallic oven casing, na cover hingedly mounted thereon, a stationary horizontal electrode mounted in said oven casing, a parallelogram linkage having its members located in a vertical plane above said electrodean'd consisting of upper'and lower longer members and a movable insulating link pivotally connected to the movable ends of said longer members, said lower longer parallelogram member being pivotally mounted on said casing and insulated therefrom and said upper parallelogram member being pivotally mounted on said cover and grounded thereto and an adjustable horizontal velectrode spaced from said stationary electrode and rigidly connected to the lower end of said insulating link and electrically connected to the movable end of said lower longer parallelogram member.A y ,v

3. In a high frequency dielectric heater, a metallic oven casing, a cover hingedly mounted thereon, a stationary horizontal electrode mount# ed in said oven casing, a parallelogram linkage having its members located in a vertical plane above said electrode and consisting of upper and lower longer members and a movable insulating link pivotally connected to the movabley ends of said longer members, said lower longer parallelogram member being pivotally mounted onv said casing and insulated therefrom and said upper parallelogram member being pivotally vmounted on said cover and grounded thereto, an adjustable horizontalelectrode spaced from said stationary electrode ,and rigidlyvconnected to the lower end of said insulating link and electrically connected to the movable end of said lower longer parallelogram member, and means mounted in said cover for adjusting the relative angular position of adjacent members of said parallelogram linkage in a vertical plane.

4. In a high frequency dielectric heater, a metallic oven casing, a cover hingedly mounted thereon, a stationary horizontal electrode mounted in Said oven casing, a parallelogram linkage having its members located in a vertical plane above said electrode and consisting of upper and lower longer members and a movable insulating link pivotally connected to the movable ends of said longer members, said lower longer parallelogram member being pivotally mounted on said casing and insulated. therefrom and said upper parallelogram member being pivotally mounted 0n said cover and grounded thereto, an adjustable horizontal electrode spaced from said stationary electrode and rigidly connected to the f lower end of said insulating link and electrically connected to the movable end of said lower longer parallelogram member and a threaded rod r0- tatably journalled in said cover and having threaded engagement with said upper parallelogram arm so as to lift same on being rotated.

5. In a high frequency dielectric heater, a metallic oven casing, a cover hingedly mounted thereon, a stationary horizontal electrode mounted on said oven casing, a parallelogram linkage having its members located in a vertical plane above said electrode and consisting of upper and lower longer members and a movable insulating link pivotally connected to the movable ends of said longer members, said lower longer parallelogram member being pivotally mounted on said casing and insulated therefrom and said upper parallelogram member being pivotally mounted on said cover and grounded thereto, an adjustable horizontal electrode spaced from said stationary electrode and rigidly connected to the lower end of said insulating link and electrically connected to the movable end of said lower longer parallelogram member, a support engaging below said upper parallelogram arm and pivotally mounted about an axis substantially in alignment with the pivotal axis of said upper parallelogram arm and a threaded rod rotatably journalled in said cover and having threaded engagement with said support so as to lower and lift same on being rotated` 6. In a high frequency dielectric heater, the combination of a metallic casing, a stationary horizontal electrode mounted in said casing and being electrically connected thereto, a parallelogram linkage arranged within said casing and having its parallel arms arranged in a vertical plane, the upper arm of said linkage being pivotally connected at one end to said casing, and the other arm of said linkage being pivotally connected at one end to an insulating member carried by said casing, a link element pivotally connected to the movable ends of said arms, a movable electrode rigidly connected to said link element and being electrically connected to the lower arm of said linkage, means connected between said casing and the upper arm of said linkage for adjusting said linkage in a vertical plane to vary the Separation between said electrodes, at least one element of said linkage interposed between said last named means and said movable electrode being formed of insulating material, and means electrically connecting the pivoted end of said lower arm to an insulated supply terminal carried by said casing.

EDMUND C. STANLEY.

REFERENCES CITED The following references are of record in the nie of this patent:

UNITED STATES PATENTS Number Name Date 1,876,106 Usselman Sept. 6, 1932 2,442,451 Albin a June 1, 1948 FOREIGN PATENTS Number Country Date 229,416 Great Britain Feb. 26, 1925 

